A/B switches are most commonly used in the electrical connections between television sets and related equipment. The A/B switch provides a means whereby an incoming television signal can be switched between two alternate signal paths, i.e., A and B. With an A/B switch installed, a viewer can switch between the two signal paths as needed without disconnecting and reconnecting the television and related equipment in a new configuration.
An example of the use of an A/B switch is illustrated in FIG. 1. FIG. 1 shows a television set 104 which is connected through an A/B switch 103 to two sources of television signals.
In this particular example, the viewer is a cable subscriber and consequently has a cable outlet 101 through which the cable television signal is provided. However, the viewer also has an antenna 102 through which a different television signal can be received. The antenna may be part of a satellite system which the viewer uses in addition to the cable system. Alternatively, the cable system may not provide over-the-air broadcast channels which the viewer can receive with the antenna.
In any event, the viewer has two sources of television signals, the cable outlet 101 and the antenna 102. By connecting both the cable outlet 101 and the antenna 102 to the A/B switch 103, the viewer can use the A/B switch to alternately connect the television 104 to the antenna 102 or the cable outlet 101 depending on what the viewer wants to watch. Without the A/B switch, the viewer would have to disconnect the television 104 from either the cable outlet 101 or the antenna 102 in order to receive the television signals from the other signal source.
Another example of the use of an A/B switch is illustrated in FIG. 2. In FIG. 2, the viewer's only source of television signals is a cable outlet 201. However, some of the channels provided by the cable system are "premium" channels. Premium channels are only available to subscribers paying additional fees and are usually scrambled to prevent unauthorized subscribers from receiving them.
In order for a subscriber to receive a premium channel, some type of decoder or descrambling device must be provided to the subscriber. Usually, the descrambler is only provided upon the payment of the additional fees for the premium channel. The subscriber then incorporates the descrambler into the connection between his television set and cable outlet so that the descrambler can unscramble the premium channel before it is received by the television set. The television set can then properly receive the premium channel.
In some cable systems, a set-top terminal 203 is used as the tuner for the cable system. In other words, the television set 206 remains tuned to a single channel. The subscriber then uses the set-top terminal 203 to change the channel being received. The set-top terminal 203 in such a system may also include the descrambler, if any, for premium channels the subscriber has paid to receive.
This creates a problem if the subscriber wishes to record a program on a premium channel while watching another, unscrambled channel. The premium channel can only be received with the aid of the descrambler in the set-top terminal 203. But then the set-top terminal 203 cannot be used to tune the other channel the viewer desires to watch.
This problem can be solved with a splitter 202 and an A/B switch 204 as illustrated in FIG. 2. The splitter 202 is connected directly to the cable outlet 201 and splits the cable signal sending it to both the A/B switch 204 and the set-top terminal 203. The set-top terminal 203 is connected to the VCR (video cassette recorder) 205 which is, in turn, connected to the A/B switch. With this configuration, the A/B switch can provide the television with either a direct signal from the cable outlet 101 via the splitter 202, or a signal from the VCR 205 via the set-top terminal 203.
Under normal circumstances, the viewer will use the set-top terminal 203 to tune the various channels available. The signal is passed with or without recording through the VCR 205 to the television set 206.
If, however, the subscriber wishes to record a premium channel while watching another, unscrambled channel, the subscriber will switch the A/B switch so that the television 206 receives a signal directly from the cable outlet 201 via the splitter 202. In this manner, the VCR 205 still receives and can record the premium channel which has been unscrambled by the set-top terminal 203. Meanwhile, the subscriber can use the television set itself to tune among the other available, unscrambled channels that he or she wishes to watch.
As seen from these two examples, A/B switches have a wide variety of applications for increase the flexibility with which television sets are connected to accompanying signal sources and equipment. However, the methods for constructing A/B switches, particularly where the A/B switch might be incorporated with or connected to a set-top terminal, remain relatively inefficient.
Consequently, there is a need in the art for an improved method of constructing an A/B switch or similar electrical switching devices.